L+R interference - KEF Reference 3 - any ideas on source?

[morethinkingcapacityneede]

Hi there. I am seeing interference between the L and R of a KEF Reference 3 pair. Seeing dips in the LF response when both speakers are playing, as well seeing a trough and a peak in the HF. I attach plots showing the effect with and without EQ. Each speaker playing separately does not show the effect.

Any ideas on possible sources and how to investigate? Is it the direct sound or reflections? I guess I should do measurements looking at the phase, however I only have a MiniDSP umik-1.

The placement isn't particularly symmetric, and there's hard-wood floor which needs a bigger rug, so probably fairly reflective. Walls are mostly bare, so probably similar situation there.

Left speaker is quite near the edge the left wall with a window, the right speaker is about 1.5m away from the right wall due to a sofa. I'm working on a drawing which I can post.

 

[morethinkingcapacityneede]

here's the EQ plot with the L+R offset by 3db to align it with the L and R measurements.

 

[ErLan]

Hi,
Based on the breif description of your setup and the wavey profile of the Lt +Rt relative to Rt, Lt saparately, I would suspect that:
A. The distances of the Lt, Rt speakers relative to MLP are slightly different (try to check via the REW alignment tool)
B. There are some phase differences in the low frequency range (<200Hz) caused by the differences in room modes profiles due to speakers asymmety speakers position/room shape (also here REW alignment tool can clarify this assumption).

Identification of the source will also help to define the possible solutions (stating the obvious )